The present invention relates to a production management system and a method of transmitting data, for use with an automatic production line for manufacturing products such as automobiles, and more particularly to a production management system having a host computer for centralized management of common data required by slave computers which are associated with pieces of production equipment such as various robots of an automobile production line and control or manage these pieces of production equipment, and a method of transmitting data in the production management system.
As more useful electronic devices are developed in recent years, production lines for manufacturing various products are being automatized to improve the quality of the manufactured products. Modern production lines include a plurality of machining stations combined with numerically controlled machine tools and automatic machines such as robots. These machining stations are coupled with an automatic warehouse or a material handling system including self-propelled carriages so that various workpieces such as parts to be machined and assembled can be automatically supplied to the machining stations. Such a combined system is known as an FA (Factory Automation) system, which includes a production management computer that controls the machining and assembling operation in each of the machining stations and controls or manages the flow or distribution of workpieces between the machining stations. The FA system is also employed to control automobile assembling lines.
To meet diverse consumer needs, some automobile assembling lines today are each designed to assemble automobiles of many different kinds based on desired combinations of types, grades, geographical regions of use, and options. It is therefore necessary on an automobile assembling line to change automatic machines or actuators frequently in all or some of the machining stations depending on the type of automobiles to be produced. Usually, the pieces of production equipment such as automatic machines of the assembling line have multiple functions and are highly complex. In order to process data to be supplied to the automatic machines and quickly recover any of the automatic machines from malfunctioning conditions, the assembling line should be controlled by a centralized production management system which manages such data processing and recovery from failures under centralized control. Highly efficient, complex data processing for an assembling line controlled by a centralized production management system preferably requires production management computers to be associated with respective pieces of production equipment in the machining (or assembling) stations for managing these pieces of production equipment under decentralized control.
On a production line such as an automobile assembling line where pieces of production equipment and actuators need to be frequently changed, however, the production management computers of such a decentralized production management system need to be separately supplied with common information such as production equipment type information, actuator type information, and abnormal code information. When certain pieces of production equipment or certain actuators are changed or removed, therefore, corresponding common information must be modified, i.e., changed in or removed from the respective associated production management computers. As a result, the maintenance of the decentralized production management system is highly complicated.
Even if the pieces of production equipment on an automobile assembling line are not changed, operation pattern data for the automatic machines in the respective machining stations must be changed each time a different automobile type is to be assembled.
The process of changing operation pattern data for the respective automatic machines on an automobile assembling line depending on the type of automobiles to be manufactured is very tedious and time-consuming, resulting in an increase in the cost of production.
The production management computers of the decentralized system are governed by a host computer. Data should be reliably and quickly transmitted between the production management computers and also between these computers and the host computer for high-speed operation of the assembling line.
FIG. 1 of the accompanying drawings shows a text format for data, which has heretofore been employed in such data transmission. The text format, generally denoted at 2, comprises a heading 4 that contains auxiliary information such as a transmission route, priority, and a message number, required to process a text, a text 6 containing an information message, transmission characters SOH (start of heading), STX (start of text), and ETX (end of text), and a block check character BCC.
The transmission control characters SOH, STX, ETX are defined by JISC 6220, and have the following functions. The transmission control character SOH is a character for starting the heading 4 of the information message. The transmission control character STX is a character used at the end of the heading 4 and prior to the text 6. The transmission control character ETX is a character used at the end of the text 6. When a data item is transmitted from a transmitting end to a receiving end, the receiving end transmits an acknowledge signal each time on of the transmission control characters SOH, STX, ETX and the block check character BCC (hereinafter referred to as transmission control characters TCC) is received, while at the same time the receiving end receives the heading 4 and the text 6.
The data transmission system in which an acknowledge signal is transmitted from the receiving end to the transmitting end each time a transmission control character TCC is received is also employed in an automobile assembling line. More specifically, data supplied to a host computer includes for example, quality control data such as tightening torque data and tightening time data from a nut runner as an automatic machine, or operation end data. Based on the supplied data, the host computer displays such quality control data on a display unit. Workpieces assembled on an automobile assembling line having a plurality of machining stations are operated upon at a large number of locations. Therefore, a vast amount of data must be transmitted and received within a short period of time.
The conventional data transmission system employing the text format 2 shown in FIG. 1 requires the transmitting and receiving ends to confirm each of the transmission control characters TCC. The time needed to confirm the transmission control characters TCC is long, and hence the time required to transmit desired data is also long. The long data transmission time tends to affect the processing time of the assembling line.